babel.config.js

let defaultPresets;
let ignorePaths = [];

// We release a ES version of Material-UI.
// It's something that matches the latest official supported features of JavaScript.
// Nothing more (stage-1, etc), nothing less (require, etc).
if (process.env.BABEL_ENV === 'es') {
  defaultPresets = [];
} else {
  defaultPresets = [
    [
      '@babel/preset-env',
      {
        modules: ['esm', 'production-umd'].includes(process.env.BABEL_ENV)
          ? false
          : 'commonjs',
      },
    ],
  ];
}

if (process.env.BABEL_ENV !== 'docz') {
  ignorePaths = [
    /@babel[\\|/]runtime/,
    'node_modules/**',
    '**/LICENCE',
    '**/README.md',
    '.mdx',
    '**/package-lock.json',
    '**/package.json',
  ];

  if (process.env.BABEL_ENV !== 'test') {
    ignorePaths.push(
      '**/*.spec.js',
      '**/*.test.js',
      /test/,
      '**/dist/**',
      '**/rollup.config.js',
    );
  }
}
// else {
//   ignorePaths = [
//     '.cache',
//   ];
// }

const productionPlugins = [
  'babel-plugin-transform-react-constant-elements',
  'babel-plugin-transform-dev-warning',
  ['babel-plugin-react-remove-properties', { properties: ['data-testid'] }],
  [
    'babel-plugin-transform-react-remove-prop-types',
    {
      mode: 'unsafe-wrap',
    },
  ],
];

module.exports = {
  presets: defaultPresets.concat(['@babel/preset-react']),
  plugins: [
    'babel-plugin-optimize-clsx',
    ['@babel/plugin-proposal-decorators', { legacy: true }],
    ['@babel/plugin-proposal-class-properties', { loose: true }],
    ['@babel/plugin-proposal-object-rest-spread', { loose: true }],
    // any package needs to declare 7.4.4 as a runtime dependency. default is ^7.0.0
    ['@babel/plugin-transform-runtime', { version: '^7.4.4' }],
    // for IE 11 support
    '@babel/plugin-transform-object-assign',
  ],
  ignore: ignorePaths,
  env: {
    cjs: {
      plugins: productionPlugins,
    },
    development: {
      plugins: [
        [
          'babel-plugin-module-resolver',
          {
            alias: {
              modules: './modules',
            },
          },
        ],
      ],
    },
    esm: {
      plugins: [
        ...productionPlugins,
        ['@babel/plugin-transform-runtime', { useESModules: true }],
      ],
    },
    es: {
      plugins: [
        ...productionPlugins,
        ['@babel/plugin-transform-runtime', { useESModules: true }],
      ],
    },
    production: {
      plugins: [
        ...productionPlugins,
        ['@babel/plugin-transform-runtime', { useESModules: true }],
      ],
    },
    'production-umd': {
      plugins: [
        ...productionPlugins,
        ['@babel/plugin-transform-runtime', { useESModules: true }],
      ],
    },
  },
};